1. Field of the Invention
The present invention relates to a key matrix circuit used in radio equipment or the like, and more particularly it relates to a circuit configuration with a minimized number of input circuits to a microcomputer circuit for recognition of selected keys, and to an associated keyboard and circuit board construction.
2. Description of the Related Art
In the past, a keyboard in which selection and setting keys are arranged in a matrix was applied to the operating panel of a transceiver or the like.
FIG. 9 shows a circuit diagram of such a keyboard, which has a 4-by-4 matrix of keys enabling selection of hexadecimal values from 0 to f.
With this key matrix circuit, there are lines 101 for the circuits 1 to 4 corresponding to the keys in the X direction (row direction), lines 102 for the circuits 5 to 8 corresponding to the keys in the Y direction (column direction), and selection keys 103 at intersections between these circuits.
The lines 101 for circuits 1 to 4 are each connected to a power supply Vcc via a resistance Rx1 to Rx4, respectively, and the lines 102 for circuits 5 to 8 are each connected to ground via a resistance Ry5 to Ry8, respectively.
Therefore, when an arbitrary selection key is set t on, a p line in the X direction and a q line in the Y direction which intersect at the key are connected, a voltage (Vd) that is divided from the power supply voltage Vcc by the resistance Rxp and Ryq is output to each circuit. The lines 101 for circuits 1 to 4 and the lines 102 for circuits 5 to 8 are connected to input ports of a microcomputer circuit, which, based on the event of the voltage on the X-direction p line and the Y-direction q line becoming the voltage Vd, recognizes which key of the 16 selection keys has been pressed, in response to which a control command or the like corresponding to the selected key is output.
Another method is the singular method shown in FIG. 10.
As shown in FIG. 10, this is the simplest system, in which if there are 16 selection keys, an on/off signal from each of the selection keys KEY1 to KEY16 is individually output to an input port of a microcomputer circuit, which monitors the state of each input port, and recognized therefrom which selection key has been pressed.
Yet another method is the A/D method shown in FIG. 11.
In this circuit, if there are 16 selection keys, the power supply voltage Vcc is connected in series to the resistances R1 to R16, and individual selection keys KEY1 to KEY16 are connected between the connection points between the resistances R1 to R16 and ground, and between the far end of resistance R16 and ground, these keys being set to on and off, and the connection point between the resistances R1 and R2 being connected to an input port of a microcomputer circuit.
With the above-noted circuit arrangement, when a key KEYp is pressed, a voltage (Vd) that is the power supply voltage Vcc divided between resistance R1 and the series resistance R1+R2+. . . +Rp) is output to the connection point between resistance R1 and resistance R2, this voltage being A/D converted by the microcomputer circuit, so as to recognize which key has been pressed, in response to the converted voltage level.
In a multiple-key input system using, for example, a ten-key pad to make various data inputs and settings in a transceiver or the like, a microcomputer circuit is used, as noted above, to perform recognition of a selected key and output of a control command and data, because of a desire to reduce the number of wiring lines and reduce the cost of components, there is a desire to use a system with a reduced number of input circuits to the microcomputer circuit and a small number of ports.
It would appear that, in response to this need, using the A/D system shown in FIG. 11, in principle only one circuit is required for a large number of selection keys, the microcomputer circuit performing recognition of what key is pressed from the voltage level after A/D conversion.
However, the usual power supply voltage Vcc of a microcomputer circuit is 5 V, and the need to achieve stable discrimination of a divided voltage imposes a requirement that a threshold be set approximately every 1 V.
Thus, in reality even the A/D system shown in FIG. 11 is limited to discrimination of five levels, or six levels if the open condition is added, so that it is not capable of discriminating the on/off states of 16 selection keys as shown in FIG. 11.
Accordingly, it is an object of the present invention to provide a key matrix circuit configuration that reduces the number of signal circuit lines to a microcomputer that performs recognition of selection keys to the minimum number, while enabling stable recognition of selected keys. It is a further object of the present invention to provide a keyboard having a construction suited to the above-noted circuit configuration.
To achieve the above-noted objects, the present invention is a key matrix circuit, having a keyboard with a plurality of selection keys arranged in an N-row-by-M-column matrix, a board having switching circuits having a first terminal and a second terminal that are connected to a common ground circuit when a corresponding selection key is pressed, the first terminals of each switching circuit, corresponding to the selected key in the row direction being connected to a first connection circuit in units of rows, and the second terminals of each switching circuit, corresponding to the selected key in the column direction being connection to a second connection circuit in units of columns, an output circuit wherein a fixed-voltage power supply and one circuit of the first connection circuits are connected by a first voltage-dividing circuit formed by a series connection of N resistances, with other first connection circuits connected to points between the other resistances of the first voltage-dividing circuit, a first output point being a resistance connection point of the first connection circuit via one resistance from the fixed-voltage power supply, and wherein a fixed-voltage power supply and one circuit of the second connection circuits are connected by a second voltage-dividing circuit formed by a series connection of M resistances, with other second connection circuits connected to points between the other resistances of the second voltage-dividing circuit, a second output point being a resistance connection point of the second connection circuit via one resistance from the fixed-voltage power supply, and a microcomputer circuit which A/D converts and captures the voltages at the first output point and the second output point of the output circuit and, using a data table, into which are stored identification data and control commands corresponding to combinations of voltage levels that the first output point can take and voltage levels that the second output point can take, these combinations being related to each selection key, performs recognition of a pressed selection key and execution of corresponding control.
According to the present invention, when a selection key is pressed, voltages that are established by the row and column to which the key belongs are output to the first output point and the second output point.
More specifically, by a switching circuit corresponding to a pressed key changing to the on state, the grounded connection location first voltage-dividing circuit and second voltage-dividing circuit, which are series resistance circuits, is set by the row and column to which the pressed key belongs, in response to which the voltage division condition which respect to the fixed-voltage power supply voltage in each of the voltage-dividing circuits is established, each of these divided voltages appearing as outputs at the first output point and the second output point.
When the above occurs, because each of the voltage-dividing circuits is a series resistance circuit, each divided voltage differs, depending upon the row and column to which the pressed selection key belongs.
The microcomputer circuit is provided with a table into which are stored identification data and control commands for each selection key of the keyboard, corresponding to combinations of the voltage level data that the first and second output points can take.
Therefore, based on the combination of the voltage level data obtained by A/D conversion of the voltages at the first output point and the second output point, there is a unique selection key that must have been pressed to result in those voltages. The microcomputer circuit access the above-noted data table to perform recognition of the pressed key, and can therefore output identification data or a control command corresponding to the recognized selection key.
The first voltage-dividing circuit and the second voltage-dividing circuit do not necessarily need to be circuits independent from the circuit board, and can alternately be formed on the same circuit board.
The configuration of the keyboard and circuit board of the present invention can take on the following forms.
In its first form, the configuration of the keyboard is one in which a electrically conductive knob contact is formed on the circuit board side of each of keys of a rubber key pad, and wherein at positions on the circuit board corresponding to each of the selection keys the first and second terminals are formed by an electrically conductive pattern, a common ground circuit being formed by a conductive pattern between the first and second terminals, and wherein the conductive patterns of the first connection circuit, the second connection circuit, and the common ground circuit are formed on the circuit board surface with insulation therebetween.
According to this form of the keyboard and circuit board, by forming the conductive patterns of the first terminal, the second terminal, the common ground circuit, and the first and second connection circuits all on the surface of the circuit board, it is possible to configure a switching circuit whereby the connection between each terminal and the common ground circuit can be switched on and off by the conductive knob contact of each selection key.
In its second form, the keyboard has knobs formed on the circuit board side of each of the selection keys of a rubber key pad, the circuit board sides of each knob having an electrically conductive surface corresponding to a common ground circuit, the circuit board having, at positions corresponding to each of the selection keys of the keyboard, a first terminal and a second terminal formed by conductive patterns, these being formed on the surface of the circuit board with mutual insulation therebetween, and a first connection circuit and a second connection circuit being insulated from the conductive surface on the keyboard side.
According to the above-noted arrangement, it is possible to provide the common ground circuit on the keyboard side, and the first and second terminals and first and second connection circuits can be formed on the circuit board side, thereby facilitating the circuit design.
In the third form of the present invention, the keyboard has knobs formed on the circuit board side of each of the selection keys of a rubber key pad and, at positions on the circuit board surface corresponding to each selection key of the keyboard, a first terminal and a second terminal are formed by conductive patterns, and conductive patterns of a first connection circuit and a second connection circuit being formed so as to be mutually insulated. Between the keyboard and the circuit board, at positions corresponding to each selection key, is formed a resilient and electrically conductive metal sheet having a part protruding toward the knob side, with an insulating layer inserted at only a joining region with respect to the circuit board surface, the resilient metal sheet being used as the common ground circuit.
According to the above-noted arrangement, it is possible to use the resilient metal sheet as the common ground circuit, there being no deformation of the conductive pattern by pressure of the selection key as is the case in the second form of the present invention, and it is further possible to have the resilience needed to return the knob be provided by the resilient metal sheet.
In the fourth form of the present invention, a first terminal and a second terminal formed at positions corresponding to the selection key on the keyboard side are formed as a single terminal, and within the path from the first connection circuit and the second connection circuit to the single terminal, a diode is inserted so that its forward direction is from each of the connection circuits to the single terminal.
According to the above-noted form of the present invention, because a switching circuit can be formed by a single terminal, on/off operations are stabilized, and a diode OR circuit can be used so that in the condition in which a selection key is not pressed, it is possible to maintain a high-impedance condition with respect to the common ground circuit.